The one thing the salesman at JJ's Pawn Shop in Beaumont, Texas, remembered about Robert Riendfliesh the day he picked up a pre-ordered load of 10 AK-47s was that he was wearing a military-style camouflage hat.

As an Army veteran of the Iraq war, Riendfliesh was intimately familiar with weapons like the deadly Romanian-made 7.62 semi-automatic, capable of discharging 30 rounds in less than a minute. But Riendfliesh, 25, wasn't buying the guns for himself.

Strapped for cash, Riendfliesh was paid $650 by a drug dealer he knew as "Manny'' for buying the rifles on Aug. 20, 2010. The dealer had assured him that the purchases were legal.

Six months later, ballistics tests proved one of the weapons Riendfliesh bought was used in the murder of ICE Agent Jaime Zapata on a Mexican highway on Feb. 15, 2011. The next day in Baytown, Texas, agents of the Bureau of Alcohol, Tobacco, Firearms and Explosives coincidentally arrested "Manny,'' Manuel Gomez Barba, the ringleader of the Baytown Crew of straw purchasers who had bought guns for Mexico's ultra-violent Zetas drug gang.

Now congressional Republicans are inquiring whether ATF's handling of the Baytown Crew investigation parallels the watch-and-wait tactics that Phoenix-based ATF agents had used in the discredited 2009-2010 Fast and Furious operation.

Court records and ATF case files in the Baytown Crew case show that while the investigation's plodding pace may have prevented agents from short-circuiting the Zapata murder-weapon purchase, there is no evidence of "gun walking'' _ trailing weapons instead of interdicting them.

"We didn't know about Barba until after the gun used in the Zapata murder was purchased," said Franceska Perot, ATF's spokeswoman in Houston and the only ATF official willing to be quoted for this story. "There was no undercover operation where we witnessed guns being purchased and let them go. That didn't happen."

Fifty pages of ATF documents obtained by Hearst Newspapers _ including a management log, reports of the investigation and timelines _ indicate that it took agents six months to arrest Barba. And it took agents more than two months _ from June 2010 to August 2010 _ to track down and interview a key witness who first identified Barba, saying he paid her $700 to purchase nine weapons at a gun show in Pasadena, Texas.

Although they knew the 26-year-old female purchaser's identity by June 7, 2010, they didn't interview her until Aug. 23, 2010 - a full three days after Barba had sent Riendfliesh to JJ'S Pawn Shop in Beaumont.

Had agents been quicker to interview the woman, they might have gotten a leg up on Barba and closed down his operation before the ill-fated Zapata murder-weapon purchase.

Issa and Grassley question why agents took so long to arrest Barba, especially when they knew early on of his drug convictions _ which automatically disqualified him from buying guns _ and that he was obliterating gun serial numbers, which is itself a crime.

Arms traffickers often remove serial numbers before sending weapons to Mexico in the belief that they can't be traced. But in fact, ATF technical experts can restore serial numbers, which is how officials traced two Texas-purchased weapons used in the Zapata murder - the one from the Baytown Crew and the other from a similar Dallas-area ring.

ATF sources said there was nothing leisurely about their pursuit of Barba and his crew. It took agents two months to interview the 26-year-old woman who was their first lead to Barba because they couldn't locate her, officials said.

ATF investigators identified six individuals who bought guns for Barba. The documents reveal that ATF interviews of Barba's straw purchasers took place weeks or months after they had bought guns for him, and there was no suggestion agents were observing transactions while closing in on Barba.

ATF officials insisted it took time for agents to gather sufficient information for a search warrant and, ultimately, a grand jury indictment.

"We don't arrest someone because a straw purchaser says 'this is the guy,''' said one ATF official. "We don't want the appearance of violating anybody's rights.''

Barba drove a black BMW and split his time between his girlfriend's Houston apartment and his parents' Baytown home. But his parents often were in Mexico, so Barba set up shop in their kitchen, grinding off weapons' serial numbers with a power tool before giving them to a man he identified as ``Veinte Uno'' _ 21 _ who paid him around $100,000 for the purchases.

"Veinte Uno'' is identified in a court document as Arturo Chavez Jr., who lives in Baytown and is a Zetas "associate.'' Chavez is now in federal custody.

One crew member recalled to agents that while he was buying six rifles for Barba, a fellow customer railed that such a large purchase was ``going to end up in the wrong hands.'' The firearms dealer dismissed the complaint, saying the crew member had passed the background check and could buy all the weapons he wanted.

A Chavez associate told agents how Chavez sent him to the home of Barba's parents to retrieve weapons loaded in a large plastic tool box. Chavez then directed the associate to drive ``down the highway'' to rendezvous with an 18-wheeler. Once the weapons were reloaded, the truck took them to Mexico.

Barba pled guilty and was sentenced to eight years in prison. His ring had purchased and exported at least 44 weapons to Mexico.